Why did Dev become suspicious when the Sanyasi returned to Dahanu?

Dev became suspicious of the Sanyasi because he returned much earlier than expected. According to the account in Chapter 40, Dev had explicitly told the Sanyasi to come back after two or four months. However, the Sanyasi reappeared in a tonga after only about one month had passed. Seeing him arrive so soon, Dev felt doubtful and wondered to his son, "It hasn't even been a full month, why has he come here already? Did he forget what was said earlier?" This premature return was the primary source of Dev's suspicion.